1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to a service composition technology for ad hoc networks, and more particularly, to providing a distributed service composition model in accordance with the characteristics of an ad hoc network.
2. Description of the Related Art
As generally known in the art, service composition refers to a tool for creating new services by using existing services. Compared to the related art infrastructure-based environments, mobile ad hoc networks have been recently spotlighted as a new type of communication paradigm in line with developments in mobile devices and wireless communication technologies.
In the case of an infrastructure-based network, a number of terminal nodes are connected to a single hub and constitute a network. The hub may be regarded as a type of repeater or base station, and Internet Protocol version 4 (IPv4) can be the only protocol used in the hub.
In contrast, an ad hoc network includes at least two devices which have wireless communication and networking abilities. Each node constituting the ad hoc network can communication with another node, which belongs to the same network, even when the latter is not within range of its own radio waves. Accordingly, intermediate nodes forward or relay packets used for data communication between source and destination nodes.
As the term “ad hoc” implies, ad hoc networks are characterized in that they are self-organized, i.e., they can consist solely of mobile devices with no separate infrastructure. In addition, they are adaptive to any type of change. More particularly, nodes alone can constitute an ad hoc network and identify other nodes in the network with no separate system administration. In contrast to related art networks, ad hoc networks need no infrastructure, including base stations, wires or cables, and routers or bridges.
Ad hoc networks are also characterized in that they may consist of different types of devices. Particularly, an ad hoc network may employ the same ad hoc communication protocol for communication between different types of devices (e.g. laptop computers, PDAs, and Internet mobile telephones).
However, the current service composition technology is, from certain points of view, unsuitable for ad hoc network-based environments. This means that the majority of service composition technologies have been developed for infrastructure-based environments, and little effort has been made to compose services in ad hoc environments.
FIG. 1 shows a service composition architecture in an infrastructure-based network. Referring to FIG. 1, n nodes 10, 20, 30, and 40 capable of executing services S1, S2, S3, . . . , Sn allocated thereto, respectively, are connected to a broker/mediator 50, which acts as a type of repeater. Typical examples of the service composition technology for an infrastructure-based network include a ninja scalable Internet service architecture (hereinafter, referred to as “ninja architecture”) and an eFlow service composition engine (hereinafter, referred to as “eFlow architecture”). As a representative service composition technology in an ad hoc network, an anamika distributed service discovery and composition system (hereinafter, referred to as “anamika”) has been introduced in the industry.
The ninja architecture plugs into a network service, which has been maintaining its original state, in order to access a fixed network service, not modify existing network services. The key element of the ninja architecture is an Automatic Patch Creation (APC) service, which is executed by a set of operators and connectors, in order to create a logical path and discover a physical service necessary to execute a task.
The eFlow architecture provides a platform for integrating different types of e-services and utilizing respective functions which constitute various kinds of electronic commerce. The eFlow architecture consists of three elements: elementary e-services, a service discovery broker, and an eFlow composition engine. The service discovery broker is adapted to discover an electronic service corresponding to a service node required by the eFlow composition engine, which contains information regarding the condition of all composite service instances.
The service composition technology in infrastructure-based environments mainly relies on a centralized composition engine in order to discover, integrate, and compose a web-based e-service. For example, the APC service of the ninja architecture and the eFlow composition engine of the eFlow architecture act as the centralized composition engine. Such a centralized architecture system is more suitable for service composition in an infrastructure-based environment. This is because the centralized architecture system is established in a fixed network, which holds information regarding the entire environment and is irrelevant to the physical position of the service. As such, the centralized architecture system is unsuitable for service composition in ad hoc network environments.
FIG. 2 shows an anamika service composition architecture in an ad hoc network. The anamika architecture shown in FIG. 2 is structured in such a manner that a service composition layer 70a and a service execution layer 70b are positioned between a network layer 90 and an application layer 60. The service composition layer 70a has a broker mediation and deputy module 71a, and the service execution module 70b has a fault recovery module 71b. 
It can be said that the anamika architecture is a distributed, fault-resistant architecture designed for interactive service composition in ad hoc networks. Two types of interactive technologies have been introduced in order to perform service composition in dynamic ad hoc environments: dynamic brokerage selection and distributed brokerage techniques, both of which are performed by the broker mediation and deputy module 71a. The fault recovery module 71b compensates for faults that occur while a service is executed. In the anamika architecture, any device can act as a broker as long as it participates in service composition, and the selected broker is in charge of the overall composition process regarding a request.
However, there is a limitation on the ability of a mobile node in an ad hoc network environment, and the task execution mode is not predetermined, but it depends on the situation. This means that the selected broker, which is in charge of the overall composition process, is overloaded.